Retinitis pigmentosa, age-related macular degeneration, and others cause visual defects and may lead to blindness at an advanced stage. Human eyes normally work such that, when light is irradiated to a retina, a light signal is converted to an electrical signal through photoreceptor cells, and this electrical signal is turned into a pulse signal through retinal ganglion cells and is transmitted to a brain. When the retinitis pigmentosa, age-related macular degeneration, and others occur, the photoreceptor cells are reduced or deadened and thus could not convert the light signal to the electrical signal. Consequently, a person would lose his vision.
In recent years, various attempts have been proposed to recover the vision of patients with vision loss from the above causes.
For example, Japanese Patent No. 3514464 discloses an invention related to an artificial vision system utilizing a retina stimulating type implant. This system is arranged such that a microphotodiode having a sensitivity to visible and infrared light is implanted under a retina to receive light of a picture image that has been amplified and modulated by a NeuronNet computer via a CCD camera, thereby providing vision.
Regarding the artificial vision system, on the other hand, an optic papilla stimulating type implant for electrically stimulating an optic nerve from surrounding portions and a brain cortex stimulating type implant for electrically stimulating a visual cortex have also been studied as well as the above retina stimulating type implant.
In the retina stimulating type implant disclosed in Japanese Patent No. 3514464 however, the microphotodiode is generally located on only a part of the retina, resulting in a problem that a visual field is extremely narrow (about 10° of a visual angle).The patient therefore could not easily distinguish the surrounding circumstances and particularly would find it difficult to visually recognize a moving object. To ensure a wide visual field, on the contrary, the microphotodiode has to be implanted in a wider area. However, the implanting operation onto a spherical retina would be hard. In the case of the retina stimulating type implant, the retina is peeled for implantation of electrodes. This would cause a problem that portions surrounding the electrode setting site are also peeled, which leads to retinal detachment after the operation.
On the other hand, the optic papilla stimulating type implant for electrically stimulating the optic nerve from the surrounding portions has a disadvantage that the number of electrodes could not be increased and therefore effective vision could not be provided. The brain cortex stimulating type implant has also a problem that an information processing system is complicated and it is hard to give stimulation close to an ordinary view.
To solve the above problems, the present invention has an object to provide an artificial vision system of an optic papilla stimulating type which is a new technique for restoring vision, capable of ensuring a wide visual field without damaging a retina.